ISR corrections to associated $HZ$ production at future Higgs factories

TL;DR

This paper assesses the impact of initial state radiation (ISR) QED corrections on associated Higgs production at future electron-positron colliders, emphasizing the importance of higher-order effects for precise Higgs property measurements.

Contribution

It applies the QED Structure Function approach to include ISR corrections in four-fermion processes, highlighting the necessity of third order collinear contributions for accuracy.

Findings

ISR corrections are significant near production threshold.

Finite third order collinear contributions are essential for precision.

Full four-fermion calculations and beam energy spread affect Higgs measurements.

Abstract

We evaluate the QED corrections due to initial state radiation (ISR) to associated Higgs boson production in electron-positron ($e^+ e^-$) annihilation at typical energies of interest for the measurement of the Higgs properties at future $e^+ e^-$ colliders, such as CEPC and FCC-ee. We apply the QED Structure Function approach to the four-fermion production process $e^+ e^- \to \mu^+ \mu^- b \bar b$, including both signal and background contributions. We emphasize the relevance of the ISR corrections particularly near threshold and show that finite third order collinear contributions are mandatory to meet the expected experimental accuracy. We analyze in turn the r\^ole played by a full four-fermion calculation and beam energy spread in precision calculations for Higgs physics at future $e^+ e^-$ colliders.